This invention is concerned with plasma discharge devices, and, more particularly, is concerned with electric switches utilizing plasma discharges.
Some electrical designs require means for interrupting a high current flow with a nearly instantaneous switching action. Consider, for example, a power source supplying current to an inductor through a closed switch. Energy is stored in the inductor until the switch is opened. Opening the switch allows the inductor to discharge its energy through any impedance which may be in shunt with the switch.
It is known for switches to utilize the conduction characteristics of plasma. Well-known plasma switching devices include spark gaps and neon lamp relaxation oscillators. A more recent device is a "Cross-field Plasma Mode Electric Conduction Control" device divulged in U.S. Pat. No. 4,322,661, issued to Harvey on Mar. 30, 1982. Apparently the Harvey device applies a magnetic field to control electron flow in a plasma discharge. The switching speed in such a device is probably limited by the inductance of the magnetic circuit. Another such plasma device is the e-beam controlled switch in which electrons are ejected into a gas to support a discharge.
According to the present invention there is provided an electric switch which is "on" during a plasma discharge through an inert gas. The discharge is extinguished by the reaction products of aluminum trichloride or aluminum tri-iodide and silicon dioxide. The specific reaction product responsible for the plasma extinction in SiCl.sub.4 or SiI.sub.4. This chemical reaction is known to those skilled in the art of discharge lamps. U.S. Pat. No. 3,586,898 issued June 22, 1971 to Speros and Smyer discussed the use of aluminum trichloride and aluminum tri-iodide in a mercury vapor lamp. It was realized that AlCl.sub.3 would gradually react with silicon on the surface of a silica envelope and release sufficient SiCl.sub.4 over a period of time to change light transmission and vapor pressure. The Speros and Smyer patent is directed towards suppressing SiCl.sub.4 generation by using non-reactive envelopes.
U.S. patent application Ser. No. 402,175, filed 7/26/82 concurrently with this, divulges a mercury-free aluminum trichloride lamp. SiCl.sub.4 is regarded as a contaminant and an aluminum silicate coated envelope is disclosed.
It is an object of this invention to provide an electric switch utilizing a plasma discharge during its "on-state" and having a nearly instantaneous transition from conducting to non-conducting conditions;
another object is to provide an electric switch utilizing a plasma chemical reaction to extinguish current flow; and
an additional object is to provide a high current switch capable of a switching rate of approximately 1 KHz.